High accuracy, high flexibility energy beam machining system

ABSTRACT

A high precision system for machining substrates by means of an energy beam includes real time digital signal processor control and a deflection system providing control, within a predetermined field of the substrate, of the angle at which the beam machines the substrate. An electron beam is used in a vacuum chamber in a preferred embodiment. The system also includes an x-y table for positioning the substrate and may have provision for detecting the x-y position and angular misregistration of the substrate. Dynamic forms and stigmator control may be used to produce a uniform beam within the field. The system allows a high speed vector machining process, which optimizes the overall system throughput by minimizing the settling time of the deflection system.

This application is a division of prior pending U.S. application Ser.No. 07/557,444, filed Jul. 23, 1990, now allowed and to issue as U.S.Pat. No. 5,124,522. Another copending divisional application based onSer. No. 07/557,444 is application Ser. No. 07/745,313, filed Aug. 15,1991.

TECHNICAL FIELD

The invention relates to methods and apparatus for machining a workpiecesuch as an electronic device substrate with the aid of a high energybeam. More particularly, in a preferred embodiment, this inventionrelates to methods and apparatus for accurately and rapidly producingholes and other features, which are smaller than those currentlyattainable by other methods, in an electronic substrate, using a realtime digital signal processor control system.

DESCRIPTION OF THE PRIOR ART

In the current manufacture of multilayer ceramic (MLC) substrates forintegrated circuit semiconductor package structures, a plurality ofceramic sheets is formed by doctor blading a slurry containing a resinbinder, a particulate ceramic material, solvents, and a plasticizer,drying the doctor bladed sheet, and blanking it into appropriate sizedsheets. Via holes are then mechanically punched for forming electricalinterconnections through the sheet. Electrically conductive paste isdeposited in the holes, and in appropriate patterns on the surface ofthe sheets, the sheets stacked and laminated, and the assemblysubsequently fired at an appropriate sintering temperature. Punching thevia holes in ceramic sheets presents formidable engineering problems inview of the small size, high density, and the complex patterns of thevia holes. Apparatus used to perform these operations are described inKranik, U.S. Pat. No. 4,425,829, and in Fleet, U.S. Pat. No. 4,821,614.

The mechanical punching technology currently used to manufacture MLCsubstrates has several limitations. The aspect ratio of a hole hastraditionally been no less than one, that is the diameter has not beenless than the thickness of the sheet to be punched. As theminiaturization of electronic devices continues, the requirement thatsmaller via holes be used increases. A certain minimum sheet thicknessis necessary, however, for the mechanical integrity of the structure.

In addition to requiring smaller diameter holes, future electronicsdevices will require that the holes be spaced closer together Use of amechanical punch at these geometries causes greatly increased embossingof the green sheet, which can greatly distort the via pattern andpositional accuracy Existing technology limits the diameter of holes inMLC substrates to approximately 3.5 mils.

Given the requirement for smaller and more closely spaced features inMLC substrates, a need exists for an apparatus and a method which useadvanced technology to manufacture substrates with the requiredgeometries. This apparatus and method must be able to accurately andrapidly machine features in these substrates in order to provide thenecessary feature geometries and yet remain competitive with existingmechanical devices such as the multiple-punch apparatus described inKranik, U.S. Pat. No. 4,425,829.

One such advanced technology candidate for machining precision featuresis a laser beam. Examples of using lasers to drill holes in electronicsubstrates are described in Lassen, U.S. Pat No. 4,544,442, and inKasner, U.S. Pat. No. 4,789,770. A system which combines a Nd:YAGmachining laser with a HeNe positioning laser to accurately locate holesand other features is described in U.S. patent application 07/428,686,filed Oct. 30, 1989.

A high-intensity, focused beam of electrons can also be used to machinefeatures Steigerwald, U.S. Pat. No. 2,793,281, discloses an apparatuswhich uses an electron beam to drill holes. An improvement on thisapparatus which use a program storage device coupled with digitaldecoders to control the drilling operation is described in Steigerwald,U.S. Pat. No. 2,989,614. Another improvement which uses a video scannerto control the drilling operation is disclosed in Schleich, U.S. Pat.No. 3,192,318.

Advances in electron beam technology have made it possible to drillprecision holes with high speed. An electron beam application forsemiconductor lithography in which a computer interface is used tocorrect beam deflection by imposing a varying electrostatic deflectiononto a predetermined magnetic deflection is disclosed in Kruppa, U.S.Pat. No. 3,644,700. High speed electron drilling of printed circuitholes is disclosed in "High-Speed and Fine-Hole Processing Technology bya Pulsed Electron Beam," July, 1987, Application Engineering.

Another computer-controlled electron beam drilling application isdisclosed in Hata, U.S. Pat. No. 4,467,170. In Hata, an electronicssubstrate is continuously translated along one axis while an electronbeam sweeps back and forth in a raster pattern along the other axis. Theextent of this sweep is limited because the hole becomes lessperpendicular to the surface of the substrate as the sweep increases,thus distorting hole accuracy.

Electron beams can also be used to machine features other than holes inelectronic substrates. The use of an electron beam to machine both viaholes and other features such as channels in a ceramic substrate isdescribed in Koste, "Electron Beam Processing of Interconnect Structuresin Multi-Layer Ceramic Modules," Metallurgical Transactions, March,1971, pp. 729-731. This machining is combined with providing a sheet oflaminate over the substrate in order to provide an integral mask for ascreening process in Koste, U.S. Pat. No. 3,956,052. Neither of thesereferences describe the manner in which the machining process iscontrolled.

Current electron beam systems use a general purpose computer for processcontrol, along with specialized interface circuits The architecture ofthese computers is not optimized for real time control. Real timecontrol requires that a processor give immediate response to aninstruction. Inability of general purpose computers to perform real timecontrol limits the effectiveness of these control systems inapplications where many process variables must be simultaneouslymonitored and controlled.

Real time control systems are computationally intensive. Conventionalcomputers and microprocessors rely on software simulation to performarithmetic operations, resulting in multiple clock cycles for a singleoperation, eliminating the possibility of real time control. Even whenthis performance is enhanced, such as with the use of an arithmeticcoprocessor, the storage of programs and data in the same space inconventional architecture dictates that data and instructions be fetchedserially. The result is that an operation such as multiplication willrequire at least three clock cycles, one for the instruction fetch andone for each of the data fetches.

Digital signal processors (DSPs) are used for specific applicationswhere computational speed and system flexibility are of primaryimportance. DSP architectures generally allow a multiplication and anaddition to be performed in a single clock cycle in response to aninstruction issued in the same clock cycle. DSPs may therefore be usedto perform real time control. If processor cycle times continue todecrease it will become possible to perform real time control with theinstructions and computations on different clock cycles, althoughcurrent DSPs do not operate in this manner. DSPs use a variety ofinternal configurations to insure that data is supplied to theirarithmetic units in a timely manner. Several of these configurations arediscussed in Martin, "Wave of advances carry DSP's to new horizons, "Computer Design, Sept. 15, 1987, pp. 69-83. By combining several DSP'sin a custom system for particular applications, maximum flexibility andspeed can be attained Use of multiple DSP's in a digital servocontroller for semiconductor wafer positioning is described inContolini, "Multiple DSP's Provide Speed for Digital Servo Control,"Computer Design, Sept. 15, 1987, pp. 87-92. A technique for theattachment of multiple DSP cards to an industrial computer for toolcontrol is disclosed in Hammond, IBM Technical Disclosure Bulletin, Vol.32, No. 5A, October, 1989, pp. 452-454.

SUMMARY OF THE INVENTION

Current energy beam machining systems show that a need exists to have aflexible real time control system which can precisely control all systemfunctions to achieve greatest accuracy and speed. Current applicationsof DSP technology do not meet this need.

It is therefore an object of the present invention to provide amachining system using an energetic beam which uses real time DSPcontrol to achieve precision machining at high speed.

It is a further object of the invention to control accurately theorientation at which this beam strikes a workpiece.

It is yet a further object of the invention to provide a method formachining a workpiece with an energetic beam which increases systemthroughput by deflecting the beam in an optimized manner to only thosepoints on the workpiece which require machining.

It is still another object of the invention to personalize electronicsubstrates with an energy beam using real time DSP control without usinga mask.

In accordance with these and other objects of the present invention, ahigh-precision system for machining substrates is provided whichincludes a source of an energy beam and means for forming, directing,and blanking the beam. The system also contains an x-y table whichsupports and positions a substrate to be machined by the beam. Animportant aspect of the system is a beam deflector for directing thebeam at a predetermined angle to the substrate. The system is controlledby real time digital signal processors which control operativesubsystems of the system.

The invention also provides a method for machining substrates with highprecision which includes the steps of positioning a substrate on an x-ytable, detecting the position of the substrate and its registrationrelative to a predetermined position, forming an electron beam oppositeto the substrate, directing the beam at a predetermined angle to thesubstrate within a predetermined field of the substrate, therebymachining the substrate, and controlling at least the forming,directing, positioning, and detecting steps with real time digitalsignal processor control.

In a more particular embodiment, the invention provides a method ofpersonalizing electronic substrates which includes the steps of applyinga laminate to the surface of a substrate, positioning the substrate onan x-y table, detecting the position of the substrate, forming anelectron beam opposite to the substrate, directing the beam at apredetermined angle to the substrate within a predetermined field of thesubstrate, thereby machining the substrate in a predetermined manner,and controlling at least the forming, directing, positioning, anddetecting with real time digital signal processor control. After thepredetermined field of the substrate is machined, the substrate istranslated to a next field of the substrate and that field is machinedusing the same steps. After all fields of the substrate have beenmachined, metallization is screened onto the substrate over thelaminate.

The foregoing and other objects, features, and advantages of theinvention will be apparent from the following more particulardescription of a preferred embodiment of the invention as illustrated inthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings forming a material part of this disclosure,

FIG. 1 is a schematic block diagram of the system comprising the presentinvention.

FIG. 2 schematically shows the focus, stigmator, and deflection opticslocated in the electron beam column.

FIG. 3 is a schematic diagram of one of the DSP cards.

FIG. 4 shows a machining field of substrate with several machiningpositions and their accompanying coordinates.

FIG. 5 schematically shows a substrate mounted on a machining fixture.

FIG. 6 is a section of FIG. 5 taken at 6--6.

FIG. 7 depicts in an exaggerated manner the astigmatism problem of anuncorrected beam within a field.

FIG. 8 depicts a substrate handling subsystem of the present invention.

FIGS. 9A-9D show the steps of a maskless substrate personalizationprocess.

FIG. 10 is a flow diagram of a procedure of the present invention whichminimized machining time.

FIG. 11 depicts a series of holes drilled in a manner which customizesthe hole profile.

FIG. 12 depicts hole inaccuracy due to non-perpendicular beamdeflection.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings in more detail and particularly referring toFIG. 1 of the invention, there is shown the machining system 20according to the present invention. The machining system 20 comprises asource 55 of an energy beam 65 and preferably includes means forforming, directing, and blanking the beam. The machining operationsperformed by the system may include, but are not limited to, drilling,removing material to form channels or the like, or sculpting aworkpiece. The beam 65 may be of a pulsed or continuous nature. For thepurposes of the present invention, the preferred high energy beam is anelectron beam with a voltage range from 60 kV to 150 kV. It should beunderstood, of course, that the choice of this electron beam is notexhaustive as there are other voltage ranges of electron beams and othertypes of beams, such as lasers, which will adequately fulfill theobjects of the present invention.

The forming means are controlled by the high voltage control 49, and mayinclude a precision power supply. In a preferred embodiment, this powersupply controls the output voltage ripple of the beam to within +/- 24 Vover a voltage range of 60 kV-120 kV, which is the primary, although notexclusive, operating range of the system of the invention. This tightlycontrolled ripple voltage allows precision control of the beam size,since the composition of the beam is directly affected by the voltageripple.

The directing means may also include a dynamic focus and stigmator 58for producing a uniform beam within a predetermined field, the functionof which will become more clearly understood hereinafter. The blankingmeans may include blanking electrodes 56, which act to shut off the beamin a predetermined manner, in response to signals from a blankingamplifier 41.

Next, the machining system comprises an x-y table 140, preferablylocated opposite to the beam source 55, which includes means forsupporting and positioning a substrate 25 to be machined by the beam.The substrate selection may include an electronics substrate, inparticular a ceramic green sheet, this example of course being forpurposes of illustration and not of limitation. The positioning meanscan translate the substrate 25 along an x-axis 26 and along a y-axis 27,although other translations and rotations are contemplated within thescope of the present invention.

The system preferably includes a vacuum chamber, the vacuum of which iscontrolled by vacuum control 48. In a preferred embodiment, the vacuumchamber is composed of a first part 53, which encloses at least theportion of the x-y table 140 providing substrate supporting means 25 ofthe x-y table 140. The second portion of the vacuum chamber comprisesthe beam column 54 and encloses the beam source 55.

A substrate handling subsystem for storing and transferring thesubstrate 25 into and out of the vacuum chamber 53 may also be provided,the handling subsystem including a handling chamber 93 in selectivevacuum contact with the vacuum chamber 53. A second substrate 52 islocated in the handling chamber 93, which replaces the substrate 25 onthe x-y table 140 when machining of the substrate 25 is complete. Theoperation of the handling subsystem will become more apparenthereinafter.

The system next may comprise means for detecting the position of thesubstrate 25 within the vacuum chamber 53. The detecting means include alaser interferometer 29 and x-y table interface 45. Beam throughdetector means 28, 43 may also be provided for determining substrateregistration relative to a predetermined position and for determiningwhen features have been machined through the substrate.

An important aspect of the system is beam deflection means for directingthe beam at a predetermined angle to the substrate 25. In many machiningapplications, such as for drilling holes in electronic substrate, thismeans is used to insure that the beam is perpendicular to the substrate.The effect of non-perpendicularity will be explained furtherhereinafter. The deflection means operate when machining within apredetermined field of the substrate and may include deflection coils 59and a telecentric lens 60. The predetermined field of the substrate mayencompass the entire substrate but is usually a small subsection of thesubstrate. The focus of the lens may be manually adjusted by focuscontrol 51.

A most important component of the present invention is the real timedigital signal processor (DSP) control means 30 for controllingoperative sub-systems of the system, which in the preferred embodimentmay include control of the forming, directing, blanking, positioning,and detecting means, as well as control of the deflection and handlingsubsystems. The use of the DSP control system allows computationalspeed, system flexibility, and real time operation not found in priorart electron beam control systems for machining applications.

In a preferred, although certainly not exclusive, embodiment, thecontrol means comprises a plurality of DSP cards 34-39 operativelyconnected by a VME bus 32, a standard industrial control bus which iswell known to those skilled in the art, to a computer 31. The VME bushardware in the preferred embodiment was supplied by BICC ElectronicsGmbh. The computer 31 provides an operator interface, the computercontaining at least substrate machining data, memory, and input/outputmeans. The computer could be a personal computer such as the PC-AT,manufactured by International Business Machines Corporation, which wasused in the preferred embodiment, with machining data downloaded from alarger host system computer. The computer could also be a largercomputer or another type of personal computer without any further datacommunication to other computers. The DSP cards are connected to andprovide operative commands to interfaces 40-50 and through theseinterfaces to the controlled subsystems of the system. The DSP cards areconnected to each other by a high speed DSP-DSP bus 33.

Another feature of the preferred embodiment of the invention is thepattern buffer means 40, which may be used to provide high speed memoryaccess of substrate machining data to the DSP card control means 30. Thepattern buffer 40 thus acts as a high speed memory bank for the DSPs,the machining data for a particular substrate being loaded into thepattern buffer 40 from the computer 31 over the VME bus 32.

The DSP control means 30 thus control the entire system's operation. Forexample, in the preferred embodiment shown in FIG. 1, the instrumentcontrol DSP 36 and the high voltage control 49 provide first controllingmeans for controlling voltage to create the beam. The dynamic focus andstigmator DSP 38 and the dynamic focus and stigmator controller 44provide second controlling means for controlling dynamic focus andastigmatism to produce a uniform beam. The pulsing display DSP 35 andthe blanking amplifier 41 provide third controlling means forcontrolling the beam blanking electrodes 56. The instrument control DSP36 and the vacuum controller 48 provide fourth controlling means forcontrolling vacuum in the vacuum chambers 53, 54. The x-y table DSP 39,the x-y table interface 45, and the laser interferometer 29 providefirst detecting means for detecting the substrate x-y position, inaddition to providing means to control x-y table movements in responseto commands to move the table from one drilling field to the next. Theregistration/learn DSP 37 and the beam through detector 43 providesecond detecting means for determining substrate registration relativeto a predetermined position. The instrument and control DSP 36, thehandler interface 46, and the vacuum controller 47 provide fifthcontrolling means for controlling the substrate handling subsystem. Themaster/deflection DSP 34 and the deflection amplifier 42 provide mastercontrolling means for controlling the deflection coils 59.

Inter-DSP communication over the DSP-DSP bus 33 in response to detectedsignals allows the control means 30 to provide, in a manner which willbecome clear hereinafter, means for calculating deflection distortioncorrection, means for calculating x-y table error correction, means forcalculating registration of the substrate relative to a predeterminedposition error correction, comparing means for accumulating thedistortion correction, the table correction, and the registrationcorrection, and for comparing the accumulated correction withpredetermined feature locations, and correcting means for correctingbeam deflection to compensate for the accumulated correction, thecorrecting means responsive to the comparing means.

FIG. 3 shows a block diagram of the DSP card 67 used in the preferredembodiment. In this embodiment, the same hardware is used for DSP cards34-39. The DSP chip 68 used was a DSP56001, manufactured by Motorola,Inc. With this DSP an instruction prefetch, a 24×24 bit multiplication,a 56 bit addition, two data moves, and two address pointer updates usingone of three types of arithmetic (linear, modulo, or reverse carry) canall be executed in a single instruction cycle. This DSP providespowerful real time control capability.

The DSP chip 68 is connected to three on-card memory banks for rapiddata manipulation, the Program Memory 75, the X memory 76, and the Ymemory 77. Data and instructions are input to these memories from theVME bus connector 72. Communication with the pattern buffer 40 is routedthrough the pattern buffer interface 140 and the DSP-Pattern connector74. Data output commands to the subsystem interfaces and controllers arerouted through the D01 141 and D02 142 interfaces and the P1 69 and P270 connectors. Data input communication to these entities is routedthrough the DI interface 143 and the P3 connector 71. The DSP-DSPinterface 144 provides random access communication to other DSP cardsthrough connector J2 73.

The beam deflection means, as hereinbefore mentioned, is critical inensuring that the beam strikes the substrate at a predetermined angle.The effect on hole accuracy when accurate control of the angle is notachieved is demonstrated in FIG. 12. In the configuration in thisfigure, it is desired that the beam 65 drill holes in the substrate 25which are perpendicular to the substrate. If deflections of the beam arenot accomplished in a manner which ensures perpendicularity, an errorwill exist in any hole which is not located along the perpendicular line145 from the beam source to the substrate.

As an example of this effect, consider a hole at an angle 1/4 133 fromthe line 145 through the substrate 25 of thickness t 134. The errordelta 135 is equal to t multiplied by tan 0, or for the small anglestypically involved, is approximately equal to t multiplied by sin 8. Incases where it is desired to drill holes as small as 1 mil with anoverall positional accuracy of 10 microns, the error introduced by thiseffect is unacceptable. For example, in Hata, U.S. Pat. No. 4,467,170,this effect limits the allowable range of deflection to +/-3 mm.

The telecentric deflection system of the current invention solves thisproblem. Referring to FIG. 2, a portion of the electron beam column 54is shown. The beam 65 is first appropriately adjusted by the dynamicstigmator 61 and dynamic focus 62. The beam then passes through thedeflection coil 59 and is deflected in response to a signal from themaster/deflection DSP 34. The deflection coil can be manuallyrotationally adjusted by knob 64, which acting through bevel gears 66,rotates the deflection coil 59, to adjust the beam deflectiondirections. The beam then enters the telecentric lens 60, which has afocal length 141 which is designed to insure that the beam 65 alwaysstrikes the substrate 25 at the same angle, within the allowed range ofdeflections. In the example shown in the figure, this angle is a rightangle to the substrate. This example, of course, is for purposes ofillustration and not of limitation. In the preferred embodiment, thisallows machining at a predetermined angle within a field of about 15 mm.It should be understood that this can be increased as necessary by anappropriate selection of lenses and deflection coils.

Having described the system hardware, the operation of the system willnow be explained in further detail. This description describes apreferred embodiment and is for purposes of illustration of theoperation of the invention, not for limitation. Referring to FIG. 8, afixture 83 containing a substrate (not shown) is placed on theload/unload shuttle 148. The fixture is then transferred through highvacuum valve 96 into handling chamber 93, which is at atmosphericpressure. After the pressure in the handling chamber 93 is equalizedwith the pressure in vacuum chamber 53, the fixture 83 and the substrateare transferred through high vacuum valve 95 onto the x-y table 140 inthe vacuum chamber 53 by transfer arm 94. Although not shown in thefigure, a machined substrate may be removed from the chamber in asimilar manner at a different vertical level of the handling chamber 93system simultaneous with the placement of the substrate 25 into thechamber 53.

The system is calibrated before machining begins. As shown in FIGS. 5and 6, the substrate 25 is mounted on the fixture 83 over a set ofprecision pins 84. The area of the substrate to be machined 88 isdivided into fields 82. As shown in FIG. 4, each field 82, has areference point 78, with coordinates x_(r) and y_(r). Referring again toFIG. 5, the fixture 83 has an x-reference point x₁ 86 and a y-referencepoint y₁ 85. It is possible that the substrate may be misregistered onthe x-y table by an angle alpha 87.

The registration error must first be calculated, which entails scanningthe beam across the substrate. Referring to FIG. 1, an attenuator 57 isplaced across the beam path in response to a signal from the attenuatorcontroller 50. The attenuator 57 blocks most of the beam energy fromcontacting the substrate while the registration scan is underway.Referring again to FIGS. 5 and 6, the precision pins 84 have a centralhole 89 and are insulated from the fixture 83 backing plate byinsulators 150. The x-y table is sequentially translated so that thelocation of each hole 89 corresponds to the predetermined center line ofthe beam. The beam scans until it actually passes through the hole 89,contacting the backing plate 83 and thus registering on the beam throughdetector 43. This hole detection means may also be used to provide anindication that a feature has been machined completely through thesubstrate. After detecting the hole 89 position for each pin 84 andreferring again to FIG. 1, the actual locations are compared with thedesired predetermined position in the registration/learn DSP 37. Anappropriate correction to the beam deflection can then be made by themaster/deflection DSP 34 for any error due to misregistration. Theattenuator 57 is then withdrawn from the beam path.

The x-y table is then translated so that the position of the substrateon the x-y table is such that the center of the beam deflection fieldcorresponds to the reference point 78. The position of Y1 85 and X1 86is detected by a laser interferometer, either by direct exposure orthrough a suitable arrangement of mirrors. This information iscommunicated to the x-y table interface 45 and the x-y table DSP 39. Theactual location thus detected is compared with the desired location andan appropriate correction calculated so that the beam deflection cancompensate for any error which may exist.

The focus and the astigmatism of the beam must also be periodicallycalibrated. Referring to FIG. 7, a field 82 of the substrate 25 isshown. Without focus and astigmatism control, any beam spot not in thecenter 90 of the field, such as those at the far right 92 and upperright 91, will not be uniform, although the variation shown in the FIG.is greatly exaggerated. An initial calibration will determine the amountof focus and astigmatism control at each point in the field, which canthen be dynamically adjusted by the dynamic focus and stigmator DSP inresponse to commands from the master deflection DSP as the beam isdeflected.

The deflection coil and telecentric lens characteristics are alsodetermined and necessary deflection distortion correction values inputto the master deflection DSP. The master deflection DSP accumulates allof these correction values and issues commands to the deflectionamplifier which deflects the beam to compensate for these accumulatedcorrections. It should be noted that although the reference positions inthe preferred embodiment for the described corrections are variouslylocated on the substrate and fixture, these positions are for purposesof illustration and not for limitation.

Once these characterizations and calibrations are performed, thesubstrate can be machined. In the preferred embodiment 1200 holes weremachined in an 8 mil thick ceramic glass sheet within 0.83 seconds witha total positional accuracy of 10 microns. Holes as small as 1 mil canbe machined in this material with the system of the present invention.The 10 micron accuracy includes positional tolerances of the fixturingas well as beam deflection tolerances.

After a field is machined, the x-y table translates to the next field.An entire green sheet containing over 100,000 holes can be machined inless than two minutes. The speed and accuracy of this system demonstratethe effectiveness of the real time DSP control system.

As seen from the preceding description of the system, the systemprovides a method of machining substrates, which may include drillingholes in a substrate using an electron beam. The first step in thismethod is positioning the substrate on an x-y table in such a manner sothat it may be machined or drilled by the beam. A further step which maybe provided is to detect the position of the substrate and itsregistration relative to a predetermined position which may be performedusing a laser interferometer and a beam through detector An electronbeam is formed opposite to the substrate. The most precise beam isformed using a power supply with a substantially +/-24 V regulatedvoltage over a voltage range of 60 kV-120 kV. The forming step may alsoinclude dynamically controlling the beam focus and astigmatism. It ispreferable to enclose at least the portion of the x-y table supportingthe substrate and the source of the beam in a vacuum chamber. The beamis directed at a predetermined angle to the substrate, thereby machiningthe substrate. For drilling, this angle is preferably a right angle tothe substrate. This directing step may be performed using deflectioncoils and a telecentric lens. At least the forming, directing,positioning, and detecting steps are controlled using real time digitalsignal processors (DSP's) The machining data may be stored in a patternbuffer in communication with the DSP's. The process may also includestoring and transferring the substrate into and out of a vacuum chamberwith a handling subsystem in selective vacuum contact with the vacuumchamber

As can be seen from the preceding description of the operation of thesystem, the controlling step may also include calculating deflectiondistortion correction, calculating x-y table error correction,calculating registration of the substrate relative to a predeterminedposition error correction, accumulating the distortion correction, thetable correction, and the registration correction, comparing theaccumulated correction with predetermined feature locations, andcorrecting beam deflection to compensate for the accumulated correctionresponsive to the comparing step.

The machining process of the present invention operates by thermalmaterial removal. In prior systems, it has been observed that whendrilling a hole the diameter of the hole decreases as the hole depthincreases. Referring to FIG. 11, hole 126 is such a tapered hole. Thisis undesirable when several substrates must be aligned and attached,since the non-uniformity of the hole may cause misregistration error.Three factors influence the thermal energy of the beam: beam voltage,beam current, and pulse width. The flexible DSP control system of thepresent invention allows variation of pulse width to achieve desiredhole profiles.

Accordingly, the present invention may further comprise selectivelypulsing the beam in response to DSP signals to machine the substrate.Varying these pulse widths allows tailoring hole profiles in apredetermined manner. Hole 127 is machined in this manner. A first pulseof a predetermined pulse width machines a portion 128 of the hole.Subsequent pulses of successively increasing pulse width are used tomachine subsequent portions 129, 130 of the hole. The final pulse of thelargest pulse width completes the hole 127. In this manner a straightwalled hole can be machined. It should be understood that the use offour pulses in the example is for purposes of illustration only and notfor the purpose of limitation.

The tapered hole 126 could also be achieved by successive pulses ofsubstantially equivalent pulse width. If a greater taper is desired,successively decreasing pulse width can be applied to produce a hole 125with portions 131, 132 of successively greater taper.

The machining process described can be accomplished in either a rasteror in a vector mode. In a raster mode the beam is deflected to eachpixel in a field and unblanked only in those pixels in which a machiningoperation is desired. This method is inefficient if the machiningfeature density is not high. For example, a 15 mm×15 mm field may have360,000 pixels but only 1,200 machined features. In this configuration,the vector mode may be more desirable. In the vector mode, the beam isdeflected to only those pixels where machining operations are required.Referring to FIG. 4, a field 82 is shown with a reference point 78 andseveral machining points 79, 80, 81. In a field such as this, vectormachining is the most efficient method.

Whenever a beam is deflected from one point to another, the machiningoperation must be delayed to account for the settling of the deflectionyoke. This settling time is a function of the yoke material anddeflection size. In the vector machining mode, it is desirable tominimize the settling time to optimize system throughput.

Referring to FIG. 10, the present invention provides a method formachining features to optimize system throughput. The first step is tofetch x-y coordinates 102 of a predetermined feature location. Thisfetch could be made from the pattern buffer of the present invention tothe master/deflection DSP, but could also be made from any memory deviceto any computational device. These coordinates are then compared 106with reference x-y coordinates 105 if the predetermined feature is thefirst feature 103 in the field, or compared with the x-y coordinates 105from the immediately preceding machined feature in the field if thepredetermined feature is not the first feature in the field to bemachined. This comparison may be achieved by subtracting X₁ from X₂ orX_(r) from X₂ and comparing the result with the difference of Y₂ and Y₁or Y₂ and Y_(r). The larger x and y translation distance is used todetermine the yoke settling time.

A settling time is then calculated. If the larger of the x and ydistances does not exceed a predetermined value 108, 107, the settlingtime is set at a fixed predetermined value 109, 111. In a preferredembodiment, the predetermined distance and time are 100 micrometers and10 microseconds, respectively. If the larger of the x and y distancesdoes exceed the predetermined value, a yoke settling time is calculatedusing a predetermined formula 110, 112. In a preferred embodiment, thesettling time is determined by multiplying the larger of the x and ytranslation distances in micrometers by 0.1 microsecond.

Once the settling time is calculated, the beam is deflected 113 to thex-y coordinates of the predetermined feature, the system waits thecalculated settling time 114, and the beam is unblanked 115, therebymachining the desired feature. If there are more features to be machinedin the field 116, this process is repeated 117 until all features in thefield are machined. If there are no more features to be machined in thefield 118, the substrate is translated 120 to the reference x-ycoordinates of the next field to be machined. The field machiningprocess is then repeated 121 for the new field. When all fields on thesubstrate are machined, the process is complete 119.

The present invention also provides a method of maskless personalizationof electronics substrates. Referring to FIG. 9, a laminate 97 is appliedto the surface of the substrate 25 in FIG. 9A. The substrate is thenpositioned on an x-y table, the position of the substrate is detected,an electron beam is formed opposite to the substrate, and the electronbeam is directed at a predetermined angle to the substrate, within apredetermined field of the substrate, thereby machining the substrate.These machined features 99, 101 are shown in FIG. 9B. At least theforming, directing, positioning, and detecting steps are controlled withreal time digital signal processor control. After the predeterminedfield is machined, the x-y table is translated to the next field of thesubstrate. The entire series of steps is repeated until all fields ofthe substrate have been machined. As shown in FIG. 9C, metallization isthen screened 98 onto the substrate 25 over the laminate 97, thelaminate acting as a mask. It may be desired, although not necessary, toremove the laminate, as shown in FIG. 9D.

While the invention has been illustrated and described with reference topreferred embodiments thereof, it is to be understood that the inventionis not limited to the precise construction herein disclosed and theright is reserved to all changes and modifications coming within thescope of the invention as defined in the appended claims.

What is claimed is:
 1. A method of personalizing electronic substratescomprising the steps of:a) applying a laminate to the surface of asubstrate; b) positioning the substrate on an x-y table; c) detectingthe position of the substrate; d) forming an electron beam opposite tothe substrate; e) directing the beam at a predetermined angle to thesubstrate, within a predetermined field of the substrate, therebymachining the substrate in a predetermined manner; f) controlling atleast the forming, directing, positioning, and detecting with real-timedigital signal processor control; g) translating the x-y table to a nextfield of the substrate; h) repeating steps c) through g) until allsubstrate fields have been machined; and i) screening metallization ontothe substrate over the laminate.
 2. The method of claim 1 furthercomprising removing the laminate from the substrate.